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The C programming language provides many standard library functions for file input and output.These functions make up the bulk of the C standard library header <stdio.h>. [1] The functionality descends from a "portable I/O package" written by Mike Lesk at Bell Labs in the early 1970s, [2] and officially became part of the Unix operating system in Version 7.
In modern POSIX compliant operating systems, a program that needs to access data from a file stored in a file system uses the read system call. The file is identified by a file descriptor that is normally obtained from a previous call to open .
In DOS and Windows (and in CP/M and many DEC operating systems such as the PDP-6 monitor, [3] RT-11, VMS or TOPS-10 [4]), reading from the terminal will never produce an EOF. Instead, programs recognize that the source is a terminal (or other "character device") and interpret a given reserved character or sequence as an end-of-file indicator ...
In the case of an interactive shell, that is usually the text terminal which initiated the program. The file descriptor for standard output is 1 (one); the POSIX <unistd.h> definition is STDOUT_FILENO; the corresponding C <stdio.h> variable is FILE* stdout; similarly, the C++ <iostream> variable is std::cout.
Using process substitution lets more than one process read the standard output of the originating process. Read this example from GNU Coreutils, tee invocation. Note: If a write to any successfully opened File operand is not successful, writes to other successfully opened File operands and standard output will continue, but the exit value will ...
The C shell can also read commands from a file, called a script. Like all Unix shells, it supports filename wildcarding, piping, here documents, command substitution, variables and control structures for condition-testing and iteration. What differentiated the C shell from others, especially in the 1980s, were its interactive features and ...
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The C standard library, sometimes referred to as libc, [1] is the standard library for the C programming language, as specified in the ISO C standard. [2] Starting from the original ANSI C standard, it was developed at the same time as the C POSIX library, which is a superset of it. [3]